Field of the Invention
This invention relates to marine seismic systems and more particularly relates to the use of rechargeable autonomous seismic nodes deployed on the seabed and the simultaneous charging systems and methods thereof.
Description of the Related Art
Marine seismic data acquisition and processing generates a profile (image) of a geophysical structure under the seafloor. Reflection seismology is a method of geophysical exploration to determine the properties of the Earth's subsurface, which is especially helpful in determining an accurate location of oil and gas reservoirs or any targeted features. Marine reflection seismology is based on using a controlled source of energy (typically acoustic energy) that sends the energy through seawater and subsurface geologic formations. The transmitted acoustic energy propagates downwardly through the subsurface as acoustic waves, also referred to as seismic waves or signals. By measuring the time it takes for the reflections or refractions to come back to seismic receivers (also known as seismic data recorders or nodes), it is possible to evaluate the depth of features causing such reflections. These features may be associated with subterranean hydrocarbon deposits or other geological structures of interest.
In general, either ocean bottom cables (OBC) or ocean bottom nodes (OBN) are placed on the seabed. For OBC systems, a cable is placed on the seabed by a surface vessel and may include a large number of seismic sensors, typically connected every 25 or 50 meters into the cable. The cable provides support to the sensors, and acts as a transmission medium for power to the sensors and data received from the sensors. One such commercial system is offered by Sercel under the name SeaRay®. Regarding OBN systems, and as compared to seismic streamers and OBC systems, OBN systems have nodes that are discrete, autonomous units (no direct connection to other nodes or to the marine vessel) where data is stored and recorded during a seismic survey. One such OBN system is offered by the Applicant under the name Trilobit®. For OBN systems, seismic data recorders are placed directly on the ocean bottom by a variety of mechanisms, including by the use of one or more of Autonomous Underwater Vehicles (AUVs), Remotely Operated Vehicles (ROVs), by dropping or diving from a surface or subsurface vessel, or by attaching autonomous nodes to a cable that is deployed behind a marine vessel.
Autonomous ocean bottom nodes are independent seismometers, and in a typical application they are self-contained units comprising a housing, frame, skeleton, or shell that includes various internal components such as geophone and hydrophone sensors, a data recording unit, a reference clock for time synchronization, and a power source. The power sources are typically battery-powered, and in some instances the batteries are rechargeable. In operation, the nodes remain on the seafloor for an extended period of time. Once the data recorders are retrieved, the data is downloaded and batteries may be replaced or recharged in preparation of the next deployment. Various designs of ocean bottom autonomous nodes are well known in the art. Prior autonomous nodes include spherical shaped nodes, cylindrical shaped nodes, and disk shaped nodes. Other prior art systems include a deployment rope/cable with integral node casings or housings for receiving autonomous seismic nodes or data recorders. Some of these devices and related methods are described in more detail in the following patents, incorporated herein by reference: U.S. Pat. Nos. 6,024,344; 7,310,287; 7,675,821; 7,646,670; 7,883,292; 8,427,900; and 8,675,446.
Typically, the power source is a battery that is a non-rechargeable battery such as lithium or alkaline. In some instances, these power sources may be rechargeable batteries. Typically, the batteries for autonomous nodes are manually replaced or recharged after the nodes are retrieved on the marine vessel. If the batteries are to be replaced, an operator generally opens or dissembles the individual node unit and removes the battery and replaces it with a new battery, along with other quality control, servicing, and data retrieval operations. If the batteries are to be recharged, the operator can open the node unit and remove the rechargeable battery and replace it with a recharged battery, or manually connect a cable separately to each node to recharge the battery (with or without removing the battery from the node). For these direct recharging connections, the cable is typically attached to an external connection on the node for battery recharging, which can also transfer data at the same time.
One known node storage system is disclosed in U.S. Pat. No. 8,050,140 (“Ray et al.”), and is incorporated herein by reference. Ray et al. discloses a method and apparatus for storing, deploying, and retrieving a plurality of seismic devices. Among other things, Ray discloses a method for retrieving data from and recharging the battery on a node while the node is stored on a storage rack. Each node sits on a storage rack adjacent an individual connector for that node. Each individual connector must be physically connected to each node and permits recorded seismic data to be extracted, the clock to be synchronized, and the power source to be recharged.
Whether manually replacing batteries or recharging batteries, either process has numerous problems, including slow recharge or replacement rate, the need for each node to have an external physical connection (which are prone to corrosion and sealing issues), and the need to physically connect each node to a physical connection for data transfer, each of which leads to overall efficiency, reliability, and operating errors. Further, the use of manpower to replace or charge the batteries is very extensive and time consuming and requires space between nodes to access and recharge the nodes. Further, conventional storage containers/modules are inefficient with lots of wasted space between the nodes (to allow operator access). A marine vessel with thousands of nodes stored and utilized would require a large number of storage containers/modules based on conventional charging techniques.
A need exists for an improved autonomous seismic node design for automated node storage, handling, deployment, and recovery. A need exists for an improved method and system for seismic node charging, and in particular one that allows for the rapid charging of a plurality of nodes in a highly automated fashion that can be utilized on a variety of marine vessels and nodes with limited operator involvement. A need exists for a seismic node design that enables large numbers of nodes to be operated in the field.